We previously found that pure cultures of mouse peritoneal macrophages, in response to a phagocytic stimulus, release large amounts of slow reacting substance (SRS) which was identified as leukotriene C (LTC), an adduct of arachidonic acid (20:4) and glutathione (GSH). A simple radioassay for SRS release by macrophages prelabeled with [3H]-20:4 has been developed in which the radiolabel content of SRS can be directly related to molar quantities from the specific activity of [3H]-20:4 in cell phospholipid. Using the radioassay, we will continue our fundamental studies on LTC synthesis by examining the functional role of macrophage complement and Fc receptors in initiation of SRS release, and the effect of macrophage activation on SRS release. Through the use of buthionine sulfoximine, a specific and nontoxic inhibitor of GSH synthesis, we will examine the role of GSH in LTC formation and the consequences on 20:4 metabolism of blocking LTC synthesis at the GSH S-transferase step. The finding that macrophages are a potent source of SRS suggests that these cells may be a source of SRS in lung. We will therefore focus on pulmonary macrophages. We will compare SRS synthesis by alveolar and lung tissue macrophages following exposure to various soluble and phagocytic stimuli, determine the structure of the product, and also compare SRS release by pulmonary macrophages from sensitized and control animals challenged with IgE antisera and specific antigen. With radiolabeled SRS, we will explore SRS metabolism by perfused lung, lung slices and pulmonary macrophages. We proposes further to determine whether other elements of the cellular immune system which contain high levels of esterfied 20:4, such as circulating blood monocytes and platelets, also synthesize SRS in response to appropriate stimuli. Through the use of homogenous cell populations and a sensitive radioassay for SRS, these experiments will provide information as to the effector role of various cell types in immediate hypersensitivity-type reactions and will have application to specific diseases such as asthma in which SRS has been linked with long-lasting broncho-constriction.